Analysts at Goldman Sachs note that news over the weekend from Shire (Nasdaq: SHPGY) that the FDA had responded to its citizen petition regarding Adderall XR generic approvability, and approved the Actavis ANDA, is positive for Watson Pharmaceuticals, Inc. (NYSE: WPI) and negative for Impax Laboratories Inc. (Nasdaq: IPXL).

"We understand that Actavis has launched, adding a full generic competitor to a market that has been divided between the brand and two supply-constrained authorized generics (IPXL and TEVA)," the analyst said.

The firm currently assumes Actavis initially captures 50% share of the market with the remaining 50% divided evenly between Shire brand and the two authorized generics. Goldman doesn't expect new entrants near term, but they will be likely by the 2nd-half of 2013.